1. Field of the Invention
The present invention relates to systems and methods for accurately stabilizing dental casts. More particularly, the present invention relates to a bracing device which temporarily secures accurately related maxillary and mandibular casts while an articulator is connected thereto and methods of stabilizing dental casts during such an operation.
2. Brief Description of the Related Art
Dentists and dental technicians frequently make dental stone casts (including diagnostic casts, working casts and master casts) which represent the patient's mouth at various stages in the clinical procedures of diagnosis and restoration. It is often necessary to place these casts on a mechanical device called an articulator that allows for a simulation of the functional relationship of the jaws, and reproduces the movements of the lower jaw (mandible). The first step in this process is to relate or position the upper cast (representing the patient's maxilla or upper jaw) on the articulator, attached with a rigid setting plaster. The lower cast (representing the patient's lower jaw or mandible) is next oriented on the articulator by relating it to the mounted upper cast. The lower cast is related to the upper cast either in a determined intercuspating relationship or through the use of a recording material, e.g., a wax or elastomeric material, placed between the patient's teeth (or between wax rims and record bases simulating future positions of denture teeth) to create a record which is then transferred to the articulator and used to position or relate the lower cast to the upper cast. This process results in a very specific positioning of the casts on the articulator in a mechanical relationship that is the same as the functional relationship of the teeth in the patient's mouth and the joints which are responsible for the functional movements of the jaw (the temporomandibular joints). These articulated stone casts are used in many ways by the dentist but most frequently are used by the dentist, student dentist or dental technician to make a prosthesis or restoration for the patient (an implant supported restoration, a crown or cap, a fixed partial denture or bridge, a removable partial denture or partial plate, or a complete denture or plate). The restoration that is made from the articulated casts must meet or occlude correctly when placed into the patient's mouth and the restoration or prosthesis must function properly against the opposing teeth and in all of the movements that the patients jaw can make. This must be accomplished such that the restoration is in harmony with the muscles of mastication (chewing muscles), temporomandibular joints (jaw joints), and the existing occlusion (bite) to allow the patient to masticate (chew) and phonate (speak) properly.
Virtually every dentist, student dentist and dental technician has experienced the consequences of improperly related casts because of the difficulty, awkwardness, lack of standardization, or ineffectiveness in relating casts using current procedures. Currently, there are at least three major concerns that need to be resolved in providing a procedure for relating the mandibular cast to the maxillary cast that will result in an improvement in the articulation process. The first concern addresses the need to develop a process that is consistently accurate regardless of the variables of recording material or mounting materials used to relate and attach the mandibular cast to the articulator. The second is to develop a process that is cost effective and efficient to use so that the procedures will be universally applied. The third is to have a set of procedures that may be conveniently accomplished by one person.
In order for the procedures to produce a consistently accurate articulation of the mandibular cast, the cast must be rigidly attached to the mounted maxillary cast when the plaster is applied to attach the lower cast to the articulator. One reason that it is necessary to rigidly secure the casts is that the plaster used to attach them to the articulator expands by a certain percentage during the setting process. This percentage expansion will vary with the material chosen. This expansion potentially changes the relationship of the casts to each other if the casts are not rigidly secured together. A second significant reason that the cast should be rigidly attached is to eliminate inadvertent movement of the cast during the plaster application procedure. The mandibular cast may be easily displaced from its relationship to the upper mounted cast as highly viscous mixed plaster is loaded onto the base of the lower cast and the articulator is closed onto the plaster to establish the articulation.
The resulting alteration in the correct relationship of the casts from either or both of the above two causes is particularly significant when the patient does not have adequate teeth that allow the dentist or technician to easily correlate and verify the intercuspating (interdigitating) position of the teeth or if significant numbers of teeth have been prepared for crowns, bridges, etc. so that the occluding (biting) surfaces of the casts can be positioned only by using an interocclusal record (made in the patients mouth and then transferred in between the casts to record the position of the patient's upper jaw or teeth to the lower jaw or teeth). In these situations it may be very difficult to verify the resulting accuracy of the articulation by visual inspection and the fabrication procedures for the restoration or prosthesis would then proceed with the casts relating in an inaccurate manner. Improperly related casts will result in a restoration or prosthesis (crown, bridge, denture) being made that has improper functional occlusion. This will prevent the opposing teeth from contacting properly and can potentially introduce pathologic forces onto the teeth and supporting bone. If the restoration is not properly adjusted, the result could include tooth mobility or loosening for the patient, bone loss around the tooth, muscle pain, and/or temporomandibular joint dysfunction (TMD). To avoid these very serious problems resulting from improper occlusion, the dentist must spend extra time with the patient adjusting the restoration. This increases the cost of the restoration to the dentist, often results in altering the treatment schedule, and requires the patient to remain in the dental chair for an extended period of time. The patient may make the assumption that the dentist is not competent or efficient in his or her prosthodontic treatment procedures as a result of this experience. The potentially negative impact of this perception on the dentist's practice and patient relations may be significant.
Another problem encountered in the articulation process is that the adhesives currently used for the purpose of securing casts together do not stick to wet or moist casts. This condition further introduces potential error in the cast relationship and adds significant time to the articulation process. The adhesive materials most commonly used to attach casts together require that the cast must dry for approximately 24 hours before the adhesive materials are applied. These traditionally used materials have further difficulty in sticking to the casts because the stone casts are porous, holding water and contaminants on the surface. The requirement for a thoroughly dry cast adds a day to the time that is required before the technician can begin to fabricate the restoration.
Another issue to consider is the need for improving the efficiency and cost effectiveness of the process of articulation. The current state of the art of relating casts together and stabilizing them is to use rigid or semirigid materials available in the laboratory or office area (pieces of broken tongue depressors, cotton tip applicators, nails, burs or bur shanks, metal rods, Popsicle.RTM. sticks, match sticks, paper clips, etc.) which are then attached to each cast using sticky wax, gray stick compound, or glue from a glue gun. Most of these materials do not adhere to wet or moist casts and none of them adhere with strength to wet or moist casts. In order to get a strong bond, a waiting period of at least a day is required to be assured that the unbound water in the stone cast has completely evaporated. Dental technicians and dentists have been known to use rubber bands wrapped around the casts to secure the relationship as the casts are placed on the articulator even though the rubber bands are elastic and do not hold a secure, rigid relationship. There are some advocates of using a technique of holding the casts together whereby the hand holds the casts while the plaster used to secure them to the articulator sets. This is a time wasting procedure of questionable practicality when a large number of casts are to be articulated by the dentist or technician.
Yet another consideration is to provide a process of articulation that is practical and efficient for one person to accomplish. The process of securing casts together can be an awkward procedure for the dentist, student dentist or technician to perform without additional assistance from a second person. The procedure is accomplished by the dentist, student dentist or technician holding the casts together with one hand while applying the wax, etc., to the casts with the other hand, all while maintaining control of the articulator in some manner, frequently by holding it between the elbow and body. This process alone can lead to errors that may not be detected until the restoration is completed and returned to the patient's mouth for clinical evaluation. It has long been evident to clinicians practicing prosthodontics that there is an established need for an easier, neater, more efficient, more predictably accurate way to secure the casts together, one that can be done very soon after the casts set to allow the restoration to be fabricated as soon as possible, and one that may be accomplished easily and accurately by one person.